Section 4.5. Summary

4.5. Summary

In this chapter, we explored the aggregate impact of multiple UWB sources on 802.11a devices, 802.11b devices, GPS receivers, and CDMA-based cellular systems, based on theoretical analysis of the uniform distribution of UWB transmitters around a victim receiver. The analyses have shown that the most damaging impact from UWB transmitters is on 802.11a WLAN devices. The reason for the large impact is that 802.11a devices overlap with the UWB transmission band assigned by the FCC and ETSI (3.1 GHz to 10.6 GHz). In contrast, 802.11b devices, GPS receivers, and cellular systems all experience out-of-band interference.

The theoretical analysis has shown that despite being out of the UWB transmission band, 802.11b devices will also suffer from UWB deployment to some extent. We also showed that the cell coverage in the presence of UWB interference is considerably smaller than in the absence of it for a specific data rate. Moreover, based on the very small user densities that result in 1 dB degradation in SINR, we concluded that UWB devices have a serious impact on WLAN devices.

Further, we've shown that there is a trade-off in using 802.11a or 802.11b devices in the presence of UWB interference based on their data rate versus distance. Because 802.11a systems reside in the main UWB transmission band, their performance degradation is more serious than 802.11b systems. We showed that the presence of UWB devices would not affect GPS receivers in acquisition mode in both urban and rural areas if their densities are limited to 300 and 100 per square kilometer, respectively. This conclusion is based on assuming FCC-regulated power restrictions for UWB devices under Part 15 unlicensed intentional radiators and a UWB bandwidth of 1 GHz. For GPS receivers in tracking mode, the maximum UWB densities for urban and rural areas were calculated as 1500 and 750 devices per square kilometer, respectively. It's important to emphasize that GPS receivers don't work well in urban areas even in the absence of UWB devices because of the presence of multipath reflections and lack of LOS signals.

In the case of CDMA-based cellular systems in rural areas, analysis has shown that the UWB device density to satisfy the current FCC Part 15 emission level (19.2 dBm for transmission of 1 GHz bandwidth) should be approximately 50 per square kilometer. The analysis also showed that in urban areas, a UWB user density of 100 devices per square kilometer provides the emission levels approximately equal to the FCC Part 15 limits. The theoretical analysis also showed that the noise power of a victim receiver operating at 2 GHz will be degraded by at least 1 dB when placed at 50 meters in the line of sight of a UWB device.